What is blastomycosis?

Definition

Blastomycosis is an infection caused by Blastomyces
dermatitidis
, a fungus typically found in soil. It is endemic to the central and
southeastern United States, Canada, and parts of Africa. This type of infection
primarily affects the lungs but may spread to other parts of the body.

Causes

B. dermatitidis is a dimorphic fungus that exists as either a mold or a yeast, depending on the environment where it is found. The fungus is in mold form in wooded areas and waterways. Inhalation of fungal spores into the lungs causes a respiratory infection known as pulmonary blastomycosis. Once inside the body, the spores transform into a phagocytosis-resistant yeast form that creates cavities and then disperses. The most common extrapulmonary site of infection is the skin, followed by the bones, the prostate and other genitourinary organs, and the brain.

Risk Factors

All ages may be affected by the disease; however, the majority of reported cases involve healthy males with an outdoor occupation
or hobby. Persons with diabetes mellitus or those with weakened immune systems, including organ transplant recipients and those on immunosuppressants, are more likely to have a severe form of the disease. Atypical for fungal infections, blastomycosis is not more likely to appear in persons with acquired immunodeficiency syndrome (AIDS).

Symptoms

Some persons with pulmonary blastomycosis are asymptomatic, while others may
have flulike symptoms that include fever, chills, myalgia, headache, cough, chest
pain, weight loss, and fatigue. Extrapulmonary blastomycosis of the skin is
indicated by ulcerated lesions on the face, neck, and extremities and is a
significant indication of the disease. As the disease progresses, pain and
lesions may occur on the bones, genitalia, parts of the
central nervous system, and organs. Persons with severe disease may show symptoms
simulating bacterial pneumonia, tuberculosis, lung cancer, or adult
respiratory
distress syndrome.

Screening and Diagnosis

Blastomycosis is a rare systemic infection. Primary care physicians often
consult with an infectious disease specialist for diagnosis and treatment.
Diagnostic tests include blood and urine analyses, tissue biopsy, sputum culture,
chest X ray, and bronchoscopy. Definitive diagnosis of blastomycosis requires
culture and analysis of infected tissue under a microscope.

Treatment and Therapy

Persons with blastomycosis should be treated based on the extent and severity of the disease. Amphotericin B and intraconazole are the drugs of choice. Oral intraconazole is recommended for persons with pulmonary blastomycosis. Intravenous amphotericin B is recommended for persons with severe disease. A blastomycosis infection has the potential to be fatal if untreated.

Prevention and Outcomes

B. dermatitidis is a microscopic airborne fungus. The best form of prevention is to avoid endemic areas where the fungus is prevalent.

Bibliography

Bradsher, Robert W. “Blastomycosis.” In Clinical Mycology, edited by William E. Dismukes, Peter G. Pappas, and Jack D. Sobel. New York: Oxford University Press, 2003.

Bradsher, Robert W., and Anupama Menon. “Blastomycosis.” In Conn’s Current Therapy 2011, edited by Robert E. Rakel, Edward T. Bope, and Rick D. Kellerman. Philadelphia: Saunders/Elsevier, 2010.

Chapman, Stanley W., and Donna C. Sullivan. “Blastomycosis.” In Harrison’s Principles of Internal Medicine, edited by Joan Butterton. 17th ed. New York: McGraw-Hill, 2008.

Levitzky, Michael G. Pulmonary Physiology. 7th ed. New York: McGraw-Hill Medical, 2007.

McKinnell, James A., and Peter G. Pappas. “Blastomycosis: New Insights into Diagnosis, Prevention, and Treatment.” In Fungal Diseases, edited by Kenneth S. Knox and George A. Sarosi. Philadelphia: Saunders/Elsevier, 2009.

Steele, Russell W., and Avinash Shetty. “Blastomycosis.” Available at http://emedicine.medscape.com/article/961731-overview.

Webster, John, and Roland Weber. Introduction to Fungi. New York: Cambridge University Press, 2007.